Question

When 1 g liquid naphthalene (C₁₀H₈) solidifies.149 joules of heat is evolved. Calculate the enthalpy of fusion of naphthalene.

Answer 1

Molar mass of naphthalene (C₁₀H₈ ) = 128 g mol^–1 When 1 g of liquid naphthalene solidified, heat evolved = 149 joules

When 1 mole, i.e., 128 g of naphthalene solidifies, heat evolved = 149 joules.

When 1 mole, i.e., 128 g of naphthalene solidifies, heat evolved = 149 × 128 joules = 19072 joules

Since fusion is reverse of solidification, therefore, heat absorbed for fusion of one mole of naphthalene = 19072 joules.

i.e., Enthalpy of fusion (Δ_fus H) = + 19072 joules/mole